Offset tricone bit



Feb. 21, 1939. 1.. E. GARFIELD 2,148,372

OFFSET TRICONE BIT Filed March 21, 1956 2 Sheds-Sheet 1 Lewis 25'Garfield INVENTOR.

A TTORNEYS.

Patented Feb. 21, 1939 UNITED STATES PATENT OFFICE.

This invention relates Lewis E. Garfield, Houston,

Tex., assignor to poration of Texas Application -March 21, 1936, SerialNo. 70,080

2 Claims.

to well drills of the.

cone type where the cutters are approximately conical in shape andsurround the ends of the shafts upon which they are mounted.

The use of three cones upon such a well drill,

while a fairly recent development, has now become quite common in theoil fields. These cones have previously been set upon the head of thedrill with the axes of the cutters pointing radially toward thelongitudinal axis of the drill head and of the well bore.

When so mounted,

the cutters have a true rolling action upon the well bottom provided theapex of the cone lies on such axis. is efiicient in its action.

Such a cone runs smoothly and It has a disadvantage,

however, that it does not cut so rapidly as it should.

It is an object of this invention to increase the speed of drilling witha three cone bit by oifsetting the axes of the cones from a radialposition relative to the head, so that the cutting teeth have more of ascraping action in rolling upon the well bottom.

It is a further object, where the rows of teeth forward advancing sideand thus enable the drill to be introduced into the hole more easily andwithout wear upon the cutter or bearings.

I also aim to position the cutters so that the thrust in drilling willbe delivered more uniformly upon the bearings best formed and positionedto carry the thrust.

In the drawings herewith Fig. 1 is a side elevation of a well drillembodying the invention.

Fig. 2 is a bottom plan view of the cutters alone, positioned as theyFig. 3 is a diagram illu are in operation. strating the position of thecutters relative the axis of the hole.

Fig. 4 is a broken section showing the relative positions of the cutterteeth where the cutter axes are not offset but the teeth interflt.

Fig. 5 is a similar s change. produced in the by offsetting cutters whercutters interfit.

ection illustrating the positions of the teeth e the teeth on adjacentThe manner in which the cutters are mounted for operation is seen inFig. 1, where the bit head I has an upwardly tapered shank 2 and threedownwardly projecting legs 3. Upon these legs are the three cones 4 somounted that their 5 apices converge toward the center of the head.

As will be seen in Fig. 2 the teeth upon each cutter are formed incircumferential rows 5 around the tapered periphery of the cone. Whilethe cutters are called cones, in practice they are not truly conical.The teeth 5 adjacent the base are on a different taper than are theteeth on the remainder of the cutter; The rows of teeth on the forwardtapered zone are formed in rows offset. longitudinally of the cone fromit corresponding rows on the adjacent cutters. Hence each cutter isformed to mate with the other two cones. The cutters may be spacedapart, as shown in Fig. 2, or they may be set close together so that theteeth on one cutter 29 may interfit between the rows of teeth on bothadjacent cutters as shown in Figs. 4 and 5.

To give the cutting teeth a more effective cutting action, I incline theaxis of each cutter in a direction forwardly and outwardly from the axisof the hole as the bit head is rotated in drilling. In Fig. 3, thecutter ,4 has its axis 1 set so that it lies tangent to an imaginarycircle 9 about the longitudinal axis 6 of the wall, the walls of whichare indicated by the circle I0. 30 The length of the 'radius of thecircle 9 may vary from 1% of an inch to 1 inches, the. good eifect ofoffsetting being obtained within these limits. The radius of the hole isshown by lines 8 for purposes of more clearly indicating the movement ofthe cutter axis from its ordinary radial position.

When the cutters are thus positioned, it will be seen that the base, orlargest diameter, ll of the cutter contacts with the wall of the hole 40at its forward advancing side and not at the central portion of thebase, as heretofore. This has the effect of giving the cutter a rollingcontact with the wall of the hole as the cutter is moved downwardly inthe well, as where it is being introduced into the well. This preventsthe scraping of the base of the cone on the wall of the well and theconsequent clogging and wear previously experienced with prior bits ofthis character.

Further the rows of teeth on the cutter have a longitudinal component ofthrust at the forward end as will be understood from Fig. 3. As thecutter is moved around the well bottom A by the rotation of the drill,it will roll on the bottom but will also have a thrust in the directionof the cutter axis I. This will not only give the cutting teeth ascraping action in rolling but will exert a force upon the cutter towardthe base. This force together with the upward thrust of the formationwill produce a component thrust which is effectively taken up by theusual roller bearings.

Where the teeth on adjacent cutters interflt, as shown in Figs. 4 and 5,I also obtain another marked advantage. Where the cutters are set withtheir axes radial instead of offset as described, the rows of teeth onadjacent cutters interflt as shown in Fig. 4. It will be seen that thespace between adjacent rows of teeth on each cutter must be wide enoughto mate with two rows of teeth, one on each of the adjacent cutters. Toprovide this space it is necessary to make the teeth, or rather the rowsof teeth, narrow. For as the teeth out tracks in concentric circles onthe well bottom, and the cones have their apices converging on the samecenter, there must be room between adjacent rows of teeth on each cutterfor two rows of teeth to pass. That is, one row of teeth on the cutterpreceding and one row on the following cutter.

Where the cutters are offset, however, the effeet is to move the rows ofteeth on each cutter farther forward relative to the corresponding rowsof teeth on the following cutter and to the rear relative to thecorresponding rows on the preceding cutter.

This can be understood with reference to the diagrammatic illustrationsin Figs. 4 and 5. These two figures are top plan sectional views, ascontrasted with the showing in Fig. 3, which is a bottom plan view. InFig. 4 the axes of the cutters 4 are radial relative to the axis of thehole. Refer to the row of teeth indicated at l2 on one of the cutters.In Fig. 4 this row of teeth is closely adjacent the row l3 on thefollowing cutter and is adjacent the row I 4 on the preceding cutter. InFig. 5 the cutter axis 1 of each cutter has been offset from the centeras described relative to Fig. 3. This throws the row of teeth' l2rearwardly relative to the row I3 on the following cutter and forwardlyaway from the row 14 on the preceding cutter. This effect is exaggeratedby the fact that the row of teeth l3 on the following cutter has alsobeen thrown away from row l2 by its being also offset. The neteffect ofthis offsetting of the cutter axes is to throw the rowsof teeth onadjacent cutters further toward the middle of the spacesbetween the rowsof teeth on adjacent cutters and thus allow more clearance. I am thusenabled to make the teethwider as indicated in the shading IS on theteeth in Fig. 5, and still have plenty of room for the teeth on adjacentcones to intermesh in operation. The bottom of the hole is thus moreeffectively cut. There are no circles of uncut bottom between the tracksout by the rows of teeth on adjacent cutters. The teeth are stronger andcut longer before becoming worn out.

As has been previously pointed out, the offsetting of the cones gives abetter cutting action of the teeth due to their scraping or ploughingaction on the bottom. The load upon the bearings in operation is moreuniformly distributed.

There is a more markedoutward thrust which keeps the cutters forcedoutwardly to cut the wall of the holeand prevent locking of the cutters.Also the rows of teeth can be made wider even where they do not interflton adjacent cutters. Each row of teeth is more than half as wide as thespace between corresponding rows of teeth on adjacent cutters. Thebottom of the hole is thus more effectively cut by the drill. Where theteeth of the cutters are interfltting a complete overlapping of thetracks of the rows of teeth on the well bottom can be obtained, thusassuring efficient and rapid action of the drill. Cutters thus mountedshow a marked increase in speed of drilling. In addition to thissuperior performance in drilling, the drill can be more easily insertedinto the well because of the rolling action of the cutters on the wallof the hole as the drill is lowered.

What I claim is:

1. In a well drill, a head rotatable on a central longitudinal axis,three approximately conical shaped cutters on the forward end thereof,the axis of each cutter being offset to the forward side of thelongitudinal axis of the drill as the drill is rotated, teeth on saidcutters arranged in rows circumferentially about the same, the rows ofteeth on each cutter interfitting between the rows of teeth on eachadjacent cutter, said teeth being more than half as wide as the spacebetween the corresponding rows of teeth adjacent cutters.

2. A three cone well drill having the axes of the cones pointed at theapex forwardly and outwardly from the longitudinal axis of the well boreas said cones are rolled about the bottom of the well, circumferentialrows of teeth on said I cones, said teeth on each cutter being offsetrelative to the corresponding rows of teeth on adjacent cutters, theoffsetting of the cutter axes acting to permit greater width of teeth inadjacent rows.

LEWIS E. GARFIELD.

